Minimizing overall package size is a key design consideration for electronics packaging. Integrated circuit technology has made impressive advances toward reducing the size of the on-chip circuits required for a given processing task. Associated electronics packaging has not kept pace with this rapid miniaturization. Advanced integrated circuit packages, including flatpack and surface mount devices, are known. However, printed circuit boards which hold the integrated circuits and other electronics components can significantly increase overall electronics package size. Even more space is used between boards when multiple circuit boards are arranged in a stack.
Current interconnect technology requires the circuit boards to be spaced relatively far apart. This space is needed, in part, to provide the electrical interconnections required between the two circuit boards. Electronic devices having several stacked printed circuit boards hence includes a large amount of empty space. This situation has stymied efforts to miniaturize a wide variety of electronic devices.
These space constraints are particularly acute in the aerospace industry. Size and weight restrictions sometimes allow very little space for avionics and other on-board electronic equipment.
In view of these problems, the inventors have recognized a strong need for an improved circuit board interconnection technique. The present inventors also recognize a need for interconnecting circuit boards in a closer spaced relationship.
One traditional way to interconnect multiple circuit boards is via the edge connector. In this approach, one edge of the circuit board is configured with a number of conductive pads. These pads are then plugged into a mating socket. Edge connectors provide mechanical mounting as well as electrical connection between adjacent circuit boards, or between circuit boards and other devices.
One problem with edge connectors is that they position circuit boards relatively wide apart. This is because the mounting sockets must be large and strong enough to support the weight of the board as well as provide electrical connections. The result is more wasted space and added weight.
The inventors have also recognized that these edge connectors require relatively long conductive paths. These paths must lead from components that are spaced throughout the board, to the edge of the board where the connector is located. The path then continues through cables from connector to connector. Longer signal paths decrease circuit speed and increase unwanted capacitance and susceptibility to electromagnetic interference. Poor conductivity can also be a problem with some of these connectors.
Other approaches, called three dimensional interconnect schemes, connect the boards in a more direct manner. One of these uses straight copper posts which extend through holes in the circuit boards. Metal spacers surrounding the posts maintain the boards in a predetermined spaced relationship. Reflow solder techniques electrically connect the copper posts in the plated-through holes.
When copper posts are used, the boards must be removed to make repairs. This requires the removal of all of the solder joints between the copper posts and the printed circuit boards. This is often a very time consuming and expensive procedure. Tight manufacturing tolerances are required in order to avoid misalignment of the plated-through holes in the boards which receive the copper posts. Also, precise board spacing can be difficult to maintain using copper posts.
Another approach to connecting printed circuit boards is the use of elastomeric connectors. These connectors are nonconductive resilient members with conductive strips applied to both sides. Elastomeric connectors are usually sandwiched between two circuit boards providing electrical contact and physical spacing therebetween. Because elastomeric connectors are not positively connected to the printed circuit board, they may easily become misaligned. Also, since only a small amount of metal can be deposited on the elastomeric member, they have correspondingly low current carrying capacity.
In view of the above, it is an object of the present invention to overcome these disadvantages, and to provide a connector which allows an improved interconnection of multiple printed circuit with minimal signal path length. It is also an object of the present invention to provide a printed circuit board connection that is self aligning and that allows the system to be easily assembled and reassembled for servicing.
Specifically, the present invention defines a printed circuit board interconnect assembly that has the following components. A plurality of circuit boards are configured so that conductive areas on facing board surfaces are disposed adjacent to each other where it is desired to electrically connect the boards to each other. A contact is placed between the two circuit boards in electrical contact with the two adjacent conductive areas. The contact provides electrical connection between the two conductive areas. The boards are then fastened or compressed together by fasteners. This compresses the contact and improves electrical contact between the contact and the boards.
In one embodiment, the contact includes a curved laminar member having first and second surfaces, each in physical contact with one of the adjacent conductive areas. A resilient substance, such as an elastomeric material, is disposed between the first and second surfaces. The contact is used to maintain a predetermined spatial relationship between the boards. The first surface of the laminar member is physically coupled to the first printed circuit board area so as to physically restrict lateral motion therebetween.
The inventors have recognized that a resilient contact of this sort can be directly compressed between conductive pads on adjacent circuit boards. Proper placement of the pads can minimize signal path length as compared to conventional edge connectors. The result is shorter path length and faster circuit operation as compared to edge connectors. Furthermore, the present invention permits the boards to be stacked closer to each other than prior techniques. The spacing is limited only by the height of the components on the board. This significantly reduces the overall size of the electronic package.